Originally manufactured by the Hydra-Matic Division of General Motors and remanufactured by J. Stemple of Groveport, Ohio (marked under grip). Most famous for its namesake automatic transmission, the Hydra-Matic Division produced two contract runs for the U.S. military using a technical data package from Colt by way of the Department of Defense. While many were made, most were destroyed at the end of their service life, the majority being saw cut and discarded as scrap. Post front and two leaf windage adjustable rear sights, with a three prong flash hider and bayonet lug on the "12" and "M (verified proof)" marked barrel, unmarked upper receiver with short casing deflector and oval forward assist, triangular handguard, checkered pistol grip, and a fixed buttstock with a ribbed buttplate. The receiver is fitted with a right handed "SAFE"/"SEMI"/"AUTO" selector, with "HYDRA-MATIC DIV./G.M. CORP./U.S.A./PROPERTY/OF U.S. GOVT./M16A1" on the left side of the magazine well over the caliber and serial number. The Stemple address has been added to the left side of the grip tang. The bolt and bolt carrier are both chrome plated, the former marked "M/P" and the latter being without forward assist serrations and featuring a "flat head" retention pin and a staked and chromed gas key.